The present disclosure relates to an electric field sensor and to an image forming apparatus provided with the electric field sensor. More particularly, the present disclosure relates to an electric field sensor including a first semiconductor layer of a first conductive type and a second semiconductor layer of a second conductive type stacked on the first semiconductor layer, and to an image forming apparatus provided with such an electric field sensor.
In conventional image forming apparatuses utilizing electrophotography, an image forming process proceeds as follows. An image carrying member such as a photosensitive drum having been electrostatically charged uniformly by a charging device is irradiated with laser light from an exposing device to form an electrostatic latent image, and toner is attached to the electrostatic latent image by a developing device to form a toner image. Then, the toner image is transferred to a sheet (recording medium), and is then subjected to fixing.
In such image forming apparatuses, a surface potential sensor is provided for detecting the surface potentials on a photosensitive drum, an intermediate transfer belt, a developing roller, and the like. Then, based on the result of detection by the surface potential sensor, the charging bias of a charging device, the developing bias of a developing device, and the like are adjusted.
In typical surface potential sensors, the surface potential on a measurement target is calculated by measuring the amount of electric charge moving through a conductive member when the conductive member is brought near an electrostatically charged object (measurement target). Electric charge is caused to move by variation in the intensity of an electric field which the conductive member receives from the electrostatically charged object; thus, when the intensity of the electric field does not vary (for example, when the conductive member is fixed), the detection voltage drops quickly due to the leakage of electric charge. Thus, by periodically varying the intensity of the electric field by use of a tuning fork or the like, a current (the amount of electric charge moving) is detected.